Transparent display device including a light guide plate formed with a plurality of concave patterns at the lower surface thereof

ABSTRACT

Disclosed is a transparent display device including a light guide plate formed with a plurality of concave patterns at the lower surface thereof to totally reflect polarized light entered in a lateral direction while transmitting natural light entered from a lower direction therethrough; a light source disposed in a lateral direction of the light guide plate to emit visible light including first and second polarized lights; a first polarizing plate disposed at a lateral portion of the light guide plate to transmit either one of the first and second polarized lights through the light guide plate; a liquid crystal panel for driving liquid crystals to change the phase of the polarized light; and a second polarizing plate for controlling an amount of the polarized light according to the changed phase of the polarized light.

CROSS-REFERENCE TO RELATED APPLICATIONS

Pursuant to 35 U.S.C. §119(a), this application claims the benefit ofKorean Application No. 10-2009-0064664, filed on Jul. 15, 2009, thecontents of which are incorporated by reference herein in its entirety.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a display device, and moreparticularly, to a transparent display device having a liquid crystalpanel.

2. Description of the Related Art

In recent years, studies on transparent display devices for allowingrear objects to be seen as well as capable of making a display thereonhave been actively carried out.

In general, a transparent display device is capable of making atransparent display in an organic light-emitting panel or plasma panelusing spontaneous light emission.

However, such a transparent display is not allowed in a liquid crystalpanel incapable of emitting spontaneous light but using backlight. It isbecause a non-transparent backlight assembly should be provided at arear surface of the panel and also polarizing plates should be providedrespectively at both front and rear surfaces of the liquid crystal panelto control the transmission of light. In particular, in the polarizingplates provided respectively at both front and rear surfaces of theliquid crystal panel, light is transmitted therethrough when liquidcrystals are driven in the liquid crystal panel, but light is in anon-transparent state when liquid crystals are not driven, and thus itmay be impossible to implement a transparent display.

Such transparent display devices may be applicable to vehicle frontglasses or house glasses to provide the user's desired information.

Therefore, the applicability of such transparent display devices isexpected to be drastically expanded. In particular, a liquid crystalpanel has wide viewing angle, high luminance, high contrast and fullcolor, and thus it is urgently required to develop a transparent displaydevice having a liquid crystal panel.

SUMMARY OF THE INVENTION

The objective of the present invention is to provide a transparentdisplay device capable of implementing a transparent display by removingthe polarizing plates and changing the structure of a light guide plate.

In order to accomplish the foregoing objective, a transparent displaydevice according to the present invention is characterized by includinga light guide plate formed with a plurality of concave patterns at thelower surface thereof to totally reflect polarized light entered in alateral direction while transmitting natural light entered from a lowerdirection therethrough; a light source disposed in a lateral directionof the light guide plate to emit visible light including a first and asecond polarized light; a first polarizing plate disposed at a lateralportion of the light guide plate to transmit either one of the first andsecond polarized lights through the light guide plate; a liquid crystalpanel for driving liquid crystals to change the phase of the polarizedlight; and a second polarizing plate for controlling an amount of thepolarized light according to the changed phase of the polarized light.

In order to accomplish the foregoing objective, a transparent displaydevice according to the present invention is characterized by includinga light guide plate formed with a plurality of concave patterns at thelower surface thereof having an inclined cross-section to totallyreflect polarized light entered in both lateral directions whiletransmitting natural light entered from a lower direction therethrough;a first and a second light source disposed in both lateral directions ofthe light guide plate to emit visible light including a first and asecond polarized light; a first and a second polarizing plate disposedat both lateral surfaces of the light guide plate to transmit either oneof the first and second polarized lights through the light guide plate;a liquid crystal panel for driving liquid crystals to change the phaseof the polarized light; and a third polarizing plate for controlling anamount of the polarized light according to the changed phase of thepolarized light.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are included to provide a furtherunderstanding of the invention and are incorporated in and constitute apart of this specification, illustrate embodiments of the invention andtogether with the description serve to explain the principles of theinvention.

In the drawings:

FIG. 1 is a schematic view illustrating a transparent display deviceaccording to an embodiment of the present invention;

FIG. 2 is a schematic cross-sectional view illustrating a transparentdisplay device according to an embodiment of the present invention;

FIG. 3 is a schematic view illustrating the change process of apolarized light generated from a light source of the transparent displaydevice according to an embodiment of the present invention;

FIG. 4 is a schematic cross-sectional view illustrating a state that thelight rays generated from a light source of the transparent displaydevice according to an embodiment of the present invention is polarizedthrough a polarizing plate and a light guide plate;

FIG. 5 is a schematic plan view illustrating concave patterns formed ata lower surface of the light guide plate of the transparent displaydevice according to an embodiment of the present invention;

FIG. 6 is a schematic view illustrating a transparent display deviceaccording to another embodiment of the present invention;

FIG. 7 is a schematic cross-sectional view illustrating a transparentdisplay device according to another embodiment of the present invention;

FIG. 8 is a schematic cross-sectional view illustrating a state that thelight rays generated from a light source of the transparent displaydevice according to another embodiment of the present invention ispolarized through a polarizing plate and a light guide plate;

FIG. 9 is a schematic plan view illustrating concave patterns formed ata lower surface of the light guide plate of the transparent displaydevice according to another embodiment of the present invention;

FIG. 10 is a schematic view illustrating a transparent display deviceaccording to still another embodiment of the present invention;

FIG. 11 is a schematic cross-sectional view illustrating a transparentdisplay device according to still another embodiment of the presentinvention;

FIG. 12 is a schematic cross-sectional view illustrating a state thatthe light rays generated from a light source of the transparent displaydevice according to still another embodiment of the present invention ispolarized through a polarizing plate and a light guide plate; and

FIG. 13 is a schematic plan view illustrating concave patterns formed ata lower surface of the light guide plate of the transparent displaydevice according to still another embodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

Hereinafter, a transparent display device according to a preferredembodiment of the present invention will be described in detail withreference to the accompanying drawings.

FIG. 1 is a schematic view illustrating a transparent display deviceaccording to an embodiment of the present invention.

FIG. 2 is a schematic cross-sectional view illustrating a transparentdisplay device according to an embodiment of the present invention.

FIG. 3 is a schematic view illustrating the change process of apolarized light generated from a light source of the transparent displaydevice according to an embodiment of the present invention.

FIG. 4 is a schematic cross-sectional view illustrating a state that thelight rays generated from a light source of the transparent displaydevice according to an embodiment of the present invention is polarizedthrough a polarizing plate and a light guide plate.

FIG. 5 is a schematic plan view illustrating concave patterns formed ata lower surface of the light guide plate of the transparent displaydevice according to an embodiment of the present invention.

Referring to FIGS. 1 and 2, a transparent display device according to anembodiment of the present invention may be configured by including alight source 10 for generating light, a first polarizing plate 30 forpolarizing the light generated from the light source, a light guideplate 20 for outputting polarized light entered through the firstpolarizing plate 30 to the front surface thereof, and a liquid crystalpanel 40 and a second polarizing plate 50 for making a display by thelight outputted to the front surface through the light guide plate 20.

Here, referring to FIG. 2, the liquid crystal panel 40 may be configuredby including a first substrate 41 having a thin-film transistor (notshown) which is a switching device and a pixel electrode electricallyconnected to the thin-film transistor; a second substrate 42 having ablack matrix 43 formed at the upper surface thereof with regularintervals to block light coming from the light source, a color filterpattern 44 formed in a region between the black matrices 43, and anovercoat layer 45 formed on the color filter patterns 44; and a liquidcrystal layer 47 inserted between the first substrate 41 and the secondsubstrate 42.

On the other hand, the light source 10 is disposed to face a lightincident surface 20 a located at a side of the light guide plate 20. Thelight source 10 may be a lamp, such as a cold cathode fluorescence(CCFL) and external electrode fluorescence lamp (EEFL), or alight-emitting diode array. At this time, the light-emitting diode arraymay be configured with a red light-emitting diode, a greenlight-emitting diode, and blue light-emitting diode, or a plurality ofwhite light-emitting diodes.

Furthermore, the light emitted from the light source 10 may include afirst polarized light (vertical polarized light) and a second polarizedlight (horizontal polarized light).

In addition, the first polarizing plate 30 is disposed to adjoin andface the light incident surface 20 a located at a side of the lightguide plate 20. In other words, the first polarizing plate 30 isdisposed between the light source 10 and the light incident surface 20 aof the light guide plate 20. At this time, the first polarizing plate 30transmits only the first polarized light from the light including thefirst polarized light and the second polarized light therethrough.

If the light emitted from the light source 10 is entered to the firstpolarizing plate 30, then only the first polarized light from the lightis transmitted by the first polarizing plate 30.

The light guide plate 20 allows the first polarized light passed throughthe first polarizing plate 30 to be entered into the liquid crystalpanel 40 at the front side.

On the other hand, referring to FIG. 3, the light emitted from the lightsource 10 may include a first and a second polarized light, and only thefirst polarized light is passed through the first polarizing plate 30,and the first polarized light is entered into the liquid crystal panel40 through the light guide plate 20, and a phase difference of the firstpolarized light is changed by driving liquid crystals in the liquidcrystal panel 40, and the amount of light passed through the secondpolarizing plate 50 is changed depending on the changed level of thephase difference to express the gradation.

Moreover, natural light coming from a lower direction of the light guideplate 20 is passed through the second polarizing plate 50 regardless ofdriving the liquid crystal panel 40, thereby allowing the user to see anobject at a lower portion of the light guide plate 20 regardless ofmaking a display.

Accordingly, light prior to entering into the light guide plate 20 ispolarized, thereby implementing a display using the polarized lightwhile maintaining a transparent state using natural light coming from alower direction of the light guide plate 20. At this time, for a lightsource of the present invention, natural light entered from a lateraldirection of the light guide plate 20 may be used as a light source ofthe present invention, and polarized light emitted by an indoor lamp maybe also used.

On the other hand, it is difficult for the light guide plate 20 touniformly distribute light over an overall surface thereof as locatedaway from the light source 10, and thus the thickness of the light guideplate 20 becomes smaller as located away from the light source 10.

Furthermore, as illustrated in FIGS. 4 and 5, the light guide plate 20is formed with a plurality of concave patterns 25 to make a uniformsurface light source by scattering the light at the lower surfacethereof. At this time, the plurality of concave patterns 25 are formedby performing laser irradiation at a lower surface of the light guideplate 20 using a separate mask (not shown) defined by the same patternshape as the concave patterns. At this time, irradiation energy,irradiation time, and the like when performing laser irradiation may beapplied differently depending on the size or kind of the product. Thetransparency and luminance of the plurality of concave patterns 25 mayvary depending on the size and interval of the patterns, and thus it isrequired to properly adjust the size and interval of the patterns.Alternatively, the concave patterns 25 may be formed using a method suchas ruggedness, etching, printing, and the like, as well as laserirradiation.

Referring to FIG. 5, it is designed such that a distance (D1) betweenthe left and right concave patterns 25 adjacent to each other in ahorizontal direction (namely, X-direction) of the plurality of concavepatterns 25 is 50-350 μm, and a distance (D2) between the upper andlower concave patterns 25 adjacent to each other in a vertical direction(namely, Y-direction) is 50-350 μm. At this time, it is preferablydesigned such that a distance (D1) between the left and right concavepatterns 25 adjacent to each other in the horizontal direction (namely,X-direction) is about 150-250 μm, and a distance (D2) between the upperand lower concave patterns 25 adjacent to each other in the verticaldirection (namely, Y-direction) is about 80-150 μm. On the other hand,it is more preferably designed such that a distance (D1) between theleft and right concave patterns 25 adjacent to each other in thehorizontal direction (namely, X-direction) is about 200-230 μm, and adistance (D2) between the upper and lower concave patterns 25 adjacentto each other in the vertical direction (namely, Y-direction) is about90-120 μm.

At this time, the intervals (D1, D2) between the concave patterns 25formed in a second region (P2) of the plurality of concave patterns 25located away from the light source 10 on the basis of a central portionof the light guide plate 20 are formed narrower than the intervals (D1,D2) between the concave patterns 25 formed in a first region (P1)thereof near to the light source 10. The intervals (D1, D2) between theconcave patterns 25 are formed narrower because the second region (P2)of the light guide plate 20 is located away from the light source 10,thereby allowing the light generated from the light source 10 to beeasily reached.

In addition, the plurality of concave patterns 25 are formed with aoval-shaped structure, and the concave patterns 25 are 50-350 μm inhorizontal length (L1) and 50-300 μm in vertical length (L2). At thistime, it is preferably designed such that a size of the concave patterns25 formed in the first region (P1) of the plurality of concave patterns25 which is located near to the light source 10 on the basis of acentral portion of the light guide plate 20 is 100-150 μm in horizontallength (L1) and 50-150 μm in vertical length (L2).

Also, it is preferably designed such that a size of the concave patterns25 formed in the first region (P2) which is located away from the lightsource 10 on the basis of a central portion of the light guide plate 20is 100-200 μm in horizontal length (L1) and 50-150 μm in vertical length(L2).

On the other hand, natural light may be entered from a lower surface ofthe light guide plate 20, and at this time the natural light may beentered to the liquid crystal panel 40 via a portion between the concavepatterns 25 of the light guide plate 20. The transparent display deviceof the invention is capable of maintaining a transparent stateregardless of whether or not being displayed by such natural light.Accordingly, an object located at a lower portion of the light guideplate is allowed to be viewed by the user at the front side.

At this time, the liquid crystal panel 40 contains liquid crystals 47,the phase of the first polarized light may be varied by driving liquidcrystals. The phase of the first polarized light that can be varied bydriving liquid crystals may have a range of 0-90 degrees.

In addition, as described above, natural light is entered to the liquidcrystal panel 40 through a lower surface of the light guide plate 20,where in the natural light may include a first polarized light and asecond polarized light. Accordingly, both first and second polarizedlights of the natural light are entered to the liquid crystal panel 40,and thus the second polarized light of the natural light is passedthrough the liquid crystal panel 40 when liquid crystals are not driven,and the first polarized light of the natural light is passed through theliquid crystal panel 40 when liquid crystals are driven. As a result, anobject located at a lower portion of the light guide plate 20 is allowedto be viewed by the user regardless of driving liquid crystals, namely,making a display.

Furthermore, the second polarizing plate 50 may have an optical axisperpendicular to the first polarizing plate 30. Therefore, the lighttransmission amount may be controlled depending on the phase of thefirst polarized light varied by driving liquid crystals. For example, incase where the phase of the first polarized light is 0 degree, then thefirst polarized light is not passed through the second polarizing plate50, but a more amount of the first polarized light can be passed throughthe second polarizing plate 50 as increasing the phase of the firstpolarized light, and thus it may be possible to obtain more gradation asincreasing the amount of the first polarized light.

On the other hand, a transparent display device according to anotherembodiment of the present invention will be described below withreference to FIGS. 6 through 9.

FIG. 6 is a schematic view illustrating a transparent display deviceaccording to another embodiment of the present invention.

FIG. 7 is a schematic cross-sectional view illustrating a transparentdisplay device according to another embodiment of the present invention.

FIG. 8 is a schematic cross-sectional view illustrating a state that thelight rays generated from a light source of the transparent displaydevice according to another embodiment of the present invention ispolarized through a polarizing plate and a light guide plate.

FIG. 9 is a schematic plan view illustrating concave patterns formed ata lower surface of the light guide plate of the transparent displaydevice according to another embodiment of the present invention.

Referring to FIGS. 6 and 7, a transparent display device according toanother embodiment of the present invention may be configured byincluding a light source 110 for generating light, a first polarizingplate 130 for polarizing the light generated from the light source, alight guide plate 120 for outputting polarized light entered through thefirst polarizing plate 130 to the front surface thereof, and a liquidcrystal panel 140 and a second polarizing plate 150 for making a displayby the light outputted to the front surface through the light guideplate 120.

Here, referring to FIG. 7, the liquid crystal panel 140 may beconfigured by including a first substrate 141 having a thin-filmtransistor (not shown) which is a switching device and a pixel electrodeelectrically connected to the thin-film transistor; a second substrate142 having a black matrix 143 formed at the upper surface thereof withregular intervals to block light coming from the light source, a colorfilter pattern 144 formed in a region between the black matrices 143,and an overcoat layer 145 formed on the color filter patterns 144; and aliquid crystal layer 147 inserted between the first substrate 141 andthe second substrate 142.

On the other hand, the light source 110 is disposed to face a lightincident surface 120 a located at a side of the light guide plate 120.The light source 110 may be a lamp, such as a cold cathode fluorescence(CCFL) and external electrode fluorescence lamp (EEFL), or alight-emitting diode array. At this time, the light-emitting diode arraymay be configured with a red light-emitting diode, a greenlight-emitting diode, and blue light-emitting diode, or a plurality ofwhite light-emitting diodes.

Furthermore, the light emitted from the light source 110 may include afirst polarized light (vertical polarized light) and a second polarizedlight (horizontal polarized light).

In addition, the first polarizing plate 130 is disposed to adjoin andface the light incident surface 120 a located at a side of the lightguide plate 120 and inclined by a predetermined angle (θ1). In otherwords, the first polarizing plate 130 is disposed between the lightsource 110 and the light incident surface 120 a of the light guide plate120. At this time, the first polarizing plate 130 transmits only thefirst polarized light from the light including the first polarized lightand the second polarized light therethrough. The inclined angle (θ1) ofthe light guide plate 120 has a range of about 35-55 degrees. At thistime, it is preferable that the inclined angle (θ1) of the light guideplate 120 has a range of about 40-50 degrees.

If the light emitted from the light source 110 is entered to the firstpolarizing plate 130, then only the first polarized light from the lightis transmitted by the first polarizing plate 130.

The light guide plate 120 allows the first polarized light passedthrough the first polarizing plate 130 to be entered into the liquidcrystal panel 140 at the front side.

On the other hand, the light emitted from the light source 110 mayinclude a first and a second polarized light, and only the firstpolarized light is passed through the first polarizing plate 130, andthe first polarized light is entered into the liquid crystal panel 140through the light guide plate 120, and a phase difference of the firstpolarized light is changed by driving liquid crystals in the liquidcrystal panel 140, and the amount of light passed through the secondpolarizing plate 150 is changed depending on the changed level of thephase difference to express the gradation.

Moreover, natural light coming from a lower direction of the light guideplate 120 is passed through the second polarizing plate 150 regardlessof driving the liquid crystal panel 140, thereby allowing the user tosee an object at a lower portion of the light guide plate 120 regardlessof making a display.

Accordingly, light prior to entering into the light guide plate 120 ispolarized, thereby implementing a display using the polarized lightwhile maintaining a transparent state using natural light coming from alower direction of the light guide plate 120. At this time, for a lightsource of the present invention, natural light entered from a lateraldirection of the light guide plate 120 may be used as a light source ofthe present invention, and polarized light emitted by an indoor lamp maybe also used.

On the other hand, it is difficult for the light guide plate 120 touniformly distribute light over an overall surface thereof as locatedaway from the light source 110, and thus the thickness of the lightguide plate 120 becomes smaller as located away from the light source110.

Furthermore, as illustrated in FIGS. 8 and 9, the light guide plate 120is formed with a plurality of concave patterns 125 to make a uniformsurface light source by scattering the light at the lower surfacethereof. At this time, the plurality of concave patterns 125 are formedby performing laser irradiation at a lower surface of the light guideplate 120 using a separate mask (not shown) defined by the same patternshape as the concave patterns. At this time, irradiation energy,irradiation time, and the like when performing laser irradiation may beapplied differently depending on the size or kind of the product. Thetransparency and luminance of the plurality of concave patterns 125 mayvary depending on the size and interval of the patterns, and thus it isrequired to properly adjust the size and interval of the patterns.

Referring to FIG. 9, it is designed such that a distance (D1) betweenthe left and right concave patterns 125 adjacent to each other in ahorizontal direction (namely, X-direction) of the plurality of concavepatterns 125 is 50-350 μm, and a distance (D2) between the upper andlower concave patterns 125 adjacent to each other in a verticaldirection (namely, Y-direction) is 50-350 μm. At this time, it ispreferably designed such that a distance (D1) between the left and rightconcave patterns 125 adjacent to each other in the horizontal direction(namely, X-direction) is about 150-250 μm, and a distance (D2) betweenthe upper and lower concave patterns 125 adjacent to each other in thevertical direction (namely, Y-direction) is about 80-150 μm. On theother hand, it is more preferably designed such that a distance (D1)between the left and right concave patterns 125 adjacent to each otherin the horizontal direction (namely, X-direction) is about 200-230 μm,and a distance (D2) between the upper and lower concave patterns 125adjacent to each other in the vertical direction (namely, Y-direction)is about 90-120 μm.

At this time, the intervals (D1, D2) between the concave patterns 125formed in a second region (P2) of the plurality of concave patterns 125located away from the light source 110 on the basis of a central portionof the light guide plate 120 are formed narrower than the intervals (D1,D2) between the concave patterns 125 formed in a first region (P1)thereof near to the light source 110. The intervals (D1, D2) between theconcave patterns 125 are formed narrower because the second region (P2)of the light guide plate 120 is located away from the light source 110,thereby allowing the light generated from the light source 110 to beeasily reached.

In addition, the plurality of concave patterns 125 are formed with aoval-shaped structure, and the concave patterns 125 are 50-350 μm inhorizontal length (L1) and 50-300 μm in vertical length (L2). At thistime, it is preferably designed such that a size of the concave patterns125 formed in the first region (P1) of the plurality of concave patterns125 which is located near to the light source 110 on the basis of acentral portion of the light guide plate 120 is 100-150 μm in horizontallength (L1) and 50-150 μm in vertical length (L2).

Also, it is preferably designed such that a size of the concave patterns125 formed in the first region (P2) which is located away from the lightsource 110 on the basis of a central portion of the light guide plate120 is 100-200 μm in horizontal length (L1) and 50-150 μm in verticallength (L2).

On the other hand, natural light may be entered from a lower surface ofthe light guide plate 120, and at this time the natural light may beentered to the liquid crystal panel 140 via a portion between theconcave patterns 125 of the light guide plate 120. The transparentdisplay device of the invention is capable of maintaining a transparentstate regardless of whether or not being displayed by such naturallight. Accordingly, an object located at a lower portion of the lightguide plate is allowed to be viewed by the user at the front side.

At this time, the liquid crystal panel 140 contains liquid crystals 147,the phase of the first polarized light may be varied by driving liquidcrystals. The phase of the first polarized light that can be varied bydriving liquid crystals may have a range of 0-90 degrees.

In addition, as described above, natural light is entered to the liquidcrystal panel 140 through a lower surface of the light guide plate 120,where in the natural light may include a first polarized light and asecond polarized light. Accordingly, both first and second polarizedlights of the natural light are entered to the liquid crystal panel 140,and thus the second polarized light of the natural light is passedthrough the liquid crystal panel 140 when liquid crystals are notdriven, and the first polarized light of the natural light is passedthrough the liquid crystal panel 140 when liquid crystals are driven. Asa result, an object located at a lower portion of the light guide plate120 is allowed to be viewed by the user regardless of driving liquidcrystals, namely, making a display.

Furthermore, the second polarizing plate 150 may have an optical axisperpendicular to the first polarizing plate 130. Therefore, the lighttransmission amount may be controlled depending on the phase of thefirst polarized light varied by driving liquid crystals. For example, incase where the phase of the first polarized light is 0 degree, then thefirst polarized light is not passed through the second polarizing plate150, but a more amount of the first polarized light can be passedthrough the second polarizing plate 150 as increasing the phase of thefirst polarized light, and thus it may be possible to obtain moregradation as increasing the amount of the first polarized light.

On the other hand, a transparent display device according to stillanother embodiment of the present invention will be described below withreference to FIGS. 10 through 13.

FIG. 10 is a schematic view illustrating a transparent display deviceaccording to still another embodiment of the present invention.

FIG. 11 is a schematic cross-sectional view illustrating a transparentdisplay device according to still another embodiment of the presentinvention.

FIG. 12 is a schematic cross-sectional view illustrating a state thatthe light rays generated from a light source of the transparent displaydevice according to still another embodiment of the present invention ispolarized through a polarizing plate and a light guide plate.

FIG. 13 is a schematic plan view illustrating concave patterns formed ata lower surface of the light guide plate of the transparent displaydevice according to still another embodiment of the present invention.

Referring to FIGS. 10 and 11, a transparent display device according tostill another embodiment of the present invention may be configured byincluding a light sources 210, 235 for generating light, firstpolarizing plates 230, 235 for polarizing the light generated from thelight sources, a light guide plate 220 for outputting polarized lightentered through the first polarizing plates 230, 235 to the frontsurface thereof, and a liquid crystal panel 240 and a second polarizingplate 250 for making a display by the light outputted to the frontsurface through the light guide plate 220.

Here, referring to FIG. 11, the liquid crystal panel 240 may beconfigured by including a first substrate 241 having a thin-filmtransistor (not shown) which is a switching device and a pixel electrodeelectrically connected to the thin-film transistor; a second substrate242 having a black matrix 243 formed at the upper surface thereof withregular intervals to block light coming from the light source, a colorfilter pattern 244 formed in a region between the black matrices 243,and an overcoat layer 245 formed on the color filter patterns 244; and aliquid crystal layer 247 inserted between the first substrate 241 andthe second substrate 242.

On the other hand, the light sources 210, 215 are disposed to faceinclined-shaped light incident surfaces 220 a, 220 b located at bothsides of the light guide plate 220. The light sources 210, 215 may be alamp, such as a cold cathode fluorescence (CCFL) and external electrodefluorescence lamp (EEFL), or a light-emitting diode array. At this time,the light-emitting diode array may be configured with a redlight-emitting diode, a green light-emitting diode, and bluelight-emitting diode, or a plurality of white light-emitting diodes.

Furthermore, the light emitted from the light sources 210, 215 mayinclude a first polarized light (vertical polarized light) and a secondpolarized light (horizontal polarized light).

In addition, the first polarizing plates 230, 235 are disposed to adjoinand face the light incident surfaces 220 a, 220 b located at both sidesof the light guide plate 220 and inclined by a predetermined angle (θ1).In other words, the first polarizing plates 230, 235 are disposedbetween the light sources 210, 215 and the light incident surfaces 220a, 220 b of the light guide plate 220. At this time, the firstpolarizing plates 230, 235 transmit only the first polarized light fromthe light including the first polarized light and the second polarizedlight therethrough. The inclined angle (θ1) of the light guide plate 220has a range of about 35-55 degrees. At this time, it is preferable thatthe inclined angle (θ1) of the light guide plate 220 has a range ofabout 40-50 degrees.

If the light emitted from the light sources 210, 215 is entered to thefirst polarizing plates 230, 235, then only the first polarized lightfrom the light is transmitted by the first polarizing plates 230, 235.

The light guide plate 220 allows the first polarized light passedthrough the first polarizing plates 230, 235 to be entered into theliquid crystal panel 240 at the front side.

On the other hand, the light emitted from the light sources 210, 215 mayinclude a first and a second polarized light, and only the firstpolarized light is passed through the first polarizing plates 230, 235,and the first polarized light is entered into the liquid crystal panel240 through the light guide plate 220, and a phase difference of thefirst polarized light is changed by driving liquid crystals in theliquid crystal panel 240, and the amount of light passed through thesecond polarizing plate 250 is changed depending on the changed level ofthe phase difference to express the gradation.

Moreover, natural light coming from a lower direction of the light guideplate 220 is passed through the second polarizing plate 250 regardlessof driving the liquid crystal panel 240, thereby allowing the user tosee an object at a lower portion of the light guide plate 220 regardlessof making a display.

Accordingly, light prior to entering into the light guide plate 220 ispolarized, thereby implementing a display using the polarized lightwhile maintaining a transparent state using natural light coming from alower direction of the light guide plate 220. At this time, for a lightsource of the present invention, natural light entered from a lateraldirection of the light guide plate 220 may be used as a light source ofthe present invention, and polarized light emitted by an indoor lamp maybe also used.

On the other hand, it is difficult for the light guide plate 220 touniformly distribute light over an overall surface thereof as locatedaway from the left and right light sources 210, 215, and thus thethickness of the light guide plate 220 becomes smaller as located awayfrom the light sources 210, 215. In other words, the thickness is formedthinner as it goes toward a central portion of the light guide plate220. In particular, a lower surface of the light guide plate 220 isformed to be inclined and smaller in the thickness as it goes toward acentral portion thereof from both sides of the light guide plate. Atthis time, an inclined angle of the lower central portion of the lightguide plate 220 is preferably formed to be smaller than 180 degrees.

Furthermore, as illustrated in FIGS. 12 and 13, the light guide plate220 is formed with a plurality of concave patterns 225 to make a uniformsurface light source by scattering the light at the lower surfacethereof. At this time, the plurality of concave patterns 225 are formedby performing laser irradiation at a lower surface of the light guideplate 220 using a separate mask (not shown) defined by the same patternshape as the concave patterns. At this time, irradiation energy,irradiation time, and the like when performing laser irradiation may beapplied differently depending on the size or kind of the product. Thetransparency and luminance of the plurality of concave patterns 225 mayvary depending on the size and interval of the patterns, and thus it isrequired to properly adjust the size and interval of the patterns.

Referring to FIG. 13, it is designed such that a distance (D1) betweenthe left and right concave patterns 225 adjacent to each other in ahorizontal direction (namely, X-direction) of the plurality of concavepatterns 225 is 50-350 μm, and a distance (D2) between the upper andlower concave patterns 225 adjacent to each other in a verticaldirection (namely, Y-direction) is 50-350 μm. At this time, it ispreferably designed such that a distance (D1) between the left and rightconcave patterns 225 adjacent to each other in the horizontal direction(namely, X-direction) is about 150-250 μm, and a distance (D2) betweenthe upper and lower concave patterns 225 adjacent to each other in thevertical direction (namely, Y-direction) is about 80-150 μm. On theother hand, it is more preferably designed such that a distance (D1)between the left and right concave patterns 225 adjacent to each otherin the horizontal direction (namely, X-direction) is about 200-230 μm,and a distance (D2) between the upper and lower concave patterns 225adjacent to each other in the vertical direction (namely, Y-direction)is about 90-120 μm.

At this time, the intervals (D1, D2) between the concave patterns 225formed in a second region (P2) of the plurality of concave patterns 225located away from the light sources 210, 215 on the basis of a centralportion of the light guide plate 120 are formed narrower than theintervals (D1, D2) between the concave patterns 225 formed in a firstregion (P1) thereof near to the light sources 210, 215. The intervals(D1, D2) between the concave patterns 225 are formed narrower becausethe second region (P2) of the light guide plate 220 is located away fromthe light sources 210, 215, thereby allowing the light generated fromthe light sources 210, 215 to be easily reached.

In addition, the plurality of concave patterns 225 are formed with aoval-shaped structure, and the concave patterns 225 are 50-350 μm inhorizontal length (L1) and 50-300 μm in vertical length (L2). At thistime, it is preferably designed such that a size of the concave patterns225 formed in the first region (P1) of the plurality of concave patterns225 which is located near to the light sources 210, 215 on the basis ofa central portion of the light guide plate 220 is 100-150 μm inhorizontal length (L1) and 50-150 μm in vertical length (L2).

Also, it is preferably designed such that a size of the concave patterns225 formed in the first region (P2) which is located away from the lightsources 210, 215 on the basis of a central portion of the light guideplate 220 is 100-200 μm in horizontal length (L1) and 50-150 μm invertical length (L2).

On the other hand, natural light may be entered from a lower surface ofthe light guide plate 220, and at this time the natural light may beentered to the liquid crystal panel 240 via a portion between theconcave patterns 225 of the light guide plate 220. The transparentdisplay device of the invention is capable of maintaining a transparentstate regardless of whether or not being displayed by such naturallight. Accordingly, an object located at a lower portion of the lightguide plate is allowed to be viewed by the user at the front side.

At this time, the liquid crystal panel 240 contains liquid crystals 247,the phase of the first polarized light may be varied by driving liquidcrystals. The phase of the first polarized light that can be varied bydriving liquid crystals may have a range of 0-90 degrees.

In addition, as described above, natural light is entered to the liquidcrystal panel 240 through a lower surface of the light guide plate 220,where in the natural light may include a first polarized light and asecond polarized light. Accordingly, both first and second polarizedlights of the natural light are entered to the liquid crystal panel 240,and thus the second polarized light of the natural light is passedthrough the liquid crystal panel 240 when liquid crystals are notdriven, and the first polarized light of the natural light is passedthrough the liquid crystal panel 240 when liquid crystals are driven. Asa result, an object located at a lower portion of the light guide plate220 is allowed to be viewed by the user regardless of driving liquidcrystals, namely, making a display.

Furthermore, the second polarizing plate 250 may have an optical axisperpendicular to the first polarizing plates 230, 235. Therefore, thelight transmission amount may be controlled depending on the phase ofthe first polarized light varied by driving liquid crystals. Forexample, in case where the phase of the first polarized light is 0degree, then the first polarized light is not passed through the secondpolarizing plate 250, but a more amount of the first polarized light canbe passed through the second polarizing plate 250 as increasing thephase of the first polarized light, and thus it may be possible toobtain more gradation as increasing the amount of the first polarizedlight.

As described above, according to the present invention, a polarizingplate disposed at an upper or lower portion is removed from thepolarizing plates that have been disposed at the upper and lowerportions of a conventional liquid crystal panel, thereby allowing theimplementation of a transparent display even in liquid crystal panelswhich were formerly considered to be impossible to realize to expand theapplicability of such liquid crystal panels.

In addition, according to the present invention, some of the polarizingplates required in the existing liquid crystal display devices and someof materials of the backlight unit (optical sheets, etc.) can beremoved, thereby reducing the production cost of a transparent displaydevice.

Although the present invention has been described with reference to thepreferred embodiments as illustrated in the drawings, these are merelyillustrative, and it should be understood by those skilled in the artthat various modifications and equivalent other embodiments of thepresent invention can be made.

What is claimed is:
 1. A transparent display device, comprising: a lightguide plate formed with a plurality of concave patterns at the lowersurface thereof to totally reflect polarized light entered in a lateraldirection while transmitting natural light entered from a lowerdirection therethrough; a light source disposed in a lateral directionof the light guide plate to emit visible light including a first and asecond polarized light; a first polarizing plate disposed at a lateralportion of the light guide plate to transmit either one of the first andsecond polarized lights through to the light guide plate; a liquidcrystal panel arranged directly above an upper surface of the lightguide plate without any intervening structure between a first substrateof the liquid crystal panel and the light guide plate, wherein theliquid crystal panel drives liquid crystals to change the phase of thepolarized light; and a second polarizing plate on a second substrate ofthe liquid crystal panel, the second polarizing plate being arranged tocontrol an amount of the polarized light according to the changed phaseof the polarized light, wherein the natural light is entered from alower surface of the light guide plate, and at this time the naturallight is entered to the liquid crystal panel via a portion between theconcave patterns of the light guide plate so that the transparentdisplay device is maintained at a transparent state regardless ofwhether or not being displayed by the natural light and an objectlocated at a lower portion of the light guide plate is allowed to beviewed by the user at the front side, wherein intervals D1 and D2between the concave patterns formed in a second region P2 of theplurality of concave patterns located away from the light source on thebasis of a central portion of the lower surface of the light guide plateare formed narrower than the intervals D1 and D2 between the concavepatterns formed in a first region P1 thereof located adjacent to thelight source, and wherein the plurality of concave patterns have anoval-shaped structure, and the concave patterns formed in the firstregion (P1) of the plurality of concave patterns which is located nearto the light source on the basis of a central portion of the light guideplate is 100-150 μm in horizontal length (L1) and 50-150 μm in verticallength (L2), and the concave patterns formed in the second region (P2)which is located away from the light source 10 on the basis of a centralportion of the light guide plate is 100-200 μm in horizontal length (L1)and 50-150 μm in vertical length (L2).
 2. The transparent display deviceof claim 1, wherein the light source is any one of a lamp, alight-emitting diode array, an indoor light, and natural light.
 3. Thetransparent display device of claim 1, wherein the light entered in alateral direction of the light guide plate is used to make a display,and the natural light entered from a lower direction of the light guideplate is used in a transparent state.
 4. The transparent display deviceof claim 1, wherein the plurality of concave patterns are formed bylaser irradiation.
 5. The transparent display device of claim 1, whereina size of the concave patterns formed in a second region of theplurality of concave patterns located away from the light source on thebasis of a central portion of the lower surface of the light guide plateis formed smaller than that of the concave patterns formed in a firstregion thereof located adjacent to the light source.
 6. The transparentdisplay device of claim 5, wherein the concave patterns formed in thefirst region are 50-350 μm in horizontal length and 50-300 μm invertical length, and the concave patterns formed in the second regionare 100-200 μm in horizontal length and 50-150 μm in vertical length. 7.The transparent display device of claim 1, wherein the interval (D1)between the left and right concave patterns adjacent to each other in ahorizontal direction (X-direction) of the plurality of concave patternsis 50-350 μm, and the interval (D2) between the upper and lower concavepatterns adjacent to each other in a vertical direction (Y-direction) is50-350 μm.
 8. The transparent display device of claim 1, wherein a lightincident surface of the light guide plate is formed with an inclinedstructure.
 9. The transparent display device of claim 8, wherein aninclined angle of the light incident surface of the light guide plate isbetween 35 and 55 degrees.